Since the discourse will touch not only what is outward, evident to all, and easily observed and judged by all, but also the innermost feelings and dispositions, especially in relation to God, the Apostle calls not only the Thessalonians as witnesses, but God also. Only God can truly know holiness, that is, piety and the fear of God. Therefore the Apostle speaks as though saying, “I call your conscience as witness, and God, the witness of my conscience.” “You are witnesses of what you saw, and God is witness of what you could not see,” says Oecumenius. “For men know only what is visible, but God knows what is hidden from men,” says Theodoret.
“How holily,” that is, piously, reverently, with the fear of God, always remembering that we perform God’s work and stand before the eyes of God. Therefore it was “without guile, without deception, without man-pleasing, without impious motives,” as Oecumenius says.
“Justly,” wronging no one, rendering to each his due, and in general acting toward others according to the whole breadth of the commandments that define this relationship.
“Blamelessly,” αμεμπτως, irreproachably, soberly, chastely, temperately, gravely, and in general in such a way that no one could complain of us, as though we indulged ourselves in anything or were not strict with ourselves.
It is evident that by the word “blamelessly” Saint Paul indicates a lawful and God-pleasing manner of conduct toward themselves. This understanding does not force the text merely to suit the usual division of human duties according to the three indicated relationships. Here it may mean the same as “soberly” in Tit 2:12. But it can in no way be taken as a concept embracing both preceding terms, “holily” and “justly,” nor as a definition of the same thing that “justly” expresses, only from the negative side. It stands in the series with the first two as a distinct part equal to them, and it should not be merged with them.
“We were among you who believe,” that is, after you received the Gospel and believed. According to Saint Chrysostom, the Apostle Paul is speaking here of his dealings with the Thessalonians. He defines the manner of his conduct among them and says, “We behaved piously, justly, and blamelessly before you who believe.” These were the characteristic features in which their conduct was to be imprinted upon the souls of the Thessalonians. It was bright, pure, and attractive to their eyes, enlightened by faith.